1. Field of the Invention
The present invention relates to a digital signal processing apparatus and a digital signal processing method corresponding to a compression encoding method for an audio signal or the like.
2. Description of the Related Art
As a related art reference of a highly efficiently encoding method for an audio signal, for example, the transform encoding method is known. The transform encoding method is one type of the block segmentation frequency band division method. In the transform encoding method, a time-base audio signal is segmented into blocks at intervals of a predetermined unit time period. The time-base signal of each block is converted into a frequency-base signal (namely, orthogonally transformed). Thus, the time-base signal is divided into a plurality of frequency bands. In each frequency band, blocks are encoded. As another related art reference, the sub band coding (SBC) method as one type of the non block-segmentation frequency band dividing method is known. In the SBC method, an audio signal is divided into a plurality of frequency bands and then encoded without segmenting a time-base audio signal into blocks at intervals of a predetermined unit time period.
As another related art reference, the highly efficiently encoding method that is a combination of the band division encoding method and the SBC method is also known. In this highly efficiently encoding method, a signal of each frequency band is orthogonally transformed into a frequency-base signal corresponding to the transform encoding method. The transformed signal is encoded in each frequency band.
As an example of the orthogonal transform method, an input audio signal is segmented into blocks at intervals of a predetermined unit time period (for each frame). Each block is transformed by for example the fast Fourier transforming (FFT) method, the discrete cosine transforming (DCT) method, or the modified DCT transforming (MDCT) method. Thus, a time-base signal is converted into a frequency-base signal.
As another related art reference, an encoding method for dividing a signal into a plurality of frequency bands, performing the MDCT process for each frequency band, normalizing generated MDCT coefficients, and quantizing the normalized data is known. Thus, with this method, the encoding process can be effectively performed.
A signal that has been encoded in one of the above-described methods is decoded in the following manner. First of all, with reference to normalization information of each frequency band, transformed coefficient data such as MDCT coefficient data is generated corresponding to a highly efficiently encoded signal. Corresponding to the transformed coefficient data, so-called inversely orthogonally transforming process is performed. Thus, time-base data is generated.
When the normalization information is changed by an adding process, a subtracting process, or the like, a reproduction level adjusting function, a filtering function, and so forth can be accomplished for a time-base signal of which highly efficiently encoded data is decoded. According to this method, since the reproduction level can be adjusted by a calculating process such as an adding process or a subtracting process, the structure of the apparatus becomes simple. In addition, since a decoding process, an encoding process, and so forth are not required, the reproduction level can be adjusted without a deterioration of the signal quality. In addition, in this method, since a decoded signal is held for a predetermined time period, part of the signal generated by the decoding process can be changed.
Conventionally, the normalization information cannot be changed on real time basis in parallel with an encoding process or a decoding process. Thus, while checking the influence of a change of the normalization information against the result of the reproducing process (for example, checking whether or not a desired level is obtained), the normalization information cannot be changed.
Therefore, an object of the present invention is to provide a digital signal processing apparatus and a digital signal processing method that allow the normalization information to be changed on real time basis in parallel with an encoding process, a decoding process, or the like.
The present invention is a reproducing apparatus, comprising a reproducing means for reproducing highly efficiently encoded data from a record medium, the highly effectively encoded data being composed of spectrum data and scale factor data, a memory means for temporarily storing the highly efficiently encoded data reproduced by the reproducing means, an operating means for causing the scale factor data of the highly efficiently encoded data stored in the memory means to be changed, a memory controlling means for controlling a write address pointer and a read address pointer so that the highly effectively encoded data is intermittently written to the memory means at a first speed and highly efficiently encoded data is read from the memory means at a second speed, the second speed being lower than the first speed, a determining means for determining whether or not the address of the highly efficiently encoded data whose scale factor data is changed corresponding to the operating means and stored in the memory means is apart from the read address by a predetermined distance, and a controlling means for canceling the change of the scale factor data when the address of the highly efficiently encoded data whose scale factor data is changed corresponding to the operating means and stored in the memory means is not apart from the read address by the predetermined distance as the determined result of the determining means.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.